Considerable care must be taken in handling semiconductor wafers since a damaged wafer may result in considerable monetary loss. The semiconductor wafers must be retained in a clean room environment, substantially free of particulate contamination to preserve the purity of the payers deposited on the wafers. The requirements of a clean room environment places additional constraints on the handling of the semiconductor wafers.
For additional protection against contaminants, the semiconductor wafer are typically retained in sealed transport containers, such as SMIF pods, as they are moved throughout the manufacturing facility to minimize any exposure to the environment outside of the processing machines. The manufacturing facility is usually organizes into a plurality of bays, each including several processing machines. After the wafers in a pod have been treated at one or more of the machines, the pod leaves the bay and is transported to the next processing bay. Thus, there is essentially two types of transport loops in the manufacturing facility—the inter-bay loop in which the pods are moved between the bays, and the intra-bay loops in which the pods are moved between the processing machines of a single bay.
In the field of semiconductor processing, the manufacturing facility is typically organized into a plurality of bays 18, each including several processing machines 16. FIG. 1 shows an example of a bay 18 with several processing machines 16 including, but not limited to, equipment for depositing films on the wafers, for cleaning and/or conditioning the wafers at various stages, and the like. As is known in the art, the entrance of a processing machine 16 often includes a load port 22. Once a pod 12 is placed on the load port 22, the load port 22 automatically forwards the pod 12 towards the processing machine 16 so that the wafers may be removed from the transport pod or other container in a protective environment. This conventional transfer system may be used with processing stations 16 which do not include a load port 22.
Various transporting systems have been employed to transport the pods from bay to bay along the inter-bay loop of a manufacturing facility. Because of the amount of traffic in the inter-bay loop of the manufacturing facility, inter-bay transport is typically accomplished via overhead transport systems. The pods are delivered to a robotic storage house, often referred to as a “stocker,” which receives the pods and automatically delivers the pods to the intra-bay loop. With some systems, the inter-bay transport system is coupled to the intra-bay transport system for direct transfer between the systems. However, direct transfer may be obtained only when a compatible, overhead transport system is used in the intra-bay loop.
Within the bays, the transport pods must be carried from machine to machine and delivered to a position where the wafers may be unloaded from the pod by the machine for processing. The machine entrance is often provided with a load port where the wafers may be automatically removed from the transport pod in a protected environment. Transferring the pods to the load port requires greater precision and control over the pod than moving the pods between inter-bay conveyor and the bays. Various methods are employed to move the transport pods between the different processing machines in a bay.
For example, many systems rely upon human workers to transfer the transport pods from port to port using a cart. The worker may manually lift the pod to the port. Alternatively, the worker may actuate a manual robotic link or other lifting device to move the pod to the port and, after processing has been completed, to return the transport pod to the cart. The worker then moves the cart to the next machine and repeats the process. Relying on human workers to transport the pods from machine to machine is time consuming and inefficient. Often, the worker will not be on hand to position a pod of fresh wafers in the load port and the machine will sit in a stand-by mode reducing the time during which the machine is operating and the overall efficiency of the processing factory. Moreover, care must be taken to ensure the lifting device is properly aligned with the load port as dropping the pod or exposing the pod to sharp jolts may damage the wafers. A means for automatically moving the transport pods between machines is desirable.
Another system of intra-bay transport relies on automatic guided vehicles (AGV's) which carry the pods between the machines and move the pods into the load port. Using AGV's reduces the need for a worker in the bay and may increase the speed at which the pods are moved through the bay. However, the size of the bay limits the number of AGV's which may operate in a single bay, leaving the machines in a stand-by mode waiting for the AGV to remove the pod of processed wafers and deposit a pod of fresh wafers in the transfer bay. An automated system which may be used to rapidly deliver pods to and remove pods from the processing machines without leaving the machines in a stand-by mode is desirable.
Overhead monorail systems are also used to transport pods along the intra-bay loop. U.S. Letters Pat. No. 6,308,818, entitled “TRANSPORT SYSTEM WITH INTEGRATED TRANSPORT CARRIER AND DIRECTORS,” issued to Bonora et al, and assigned to Asyst Technologies, Inc. is an example of such a system, and is incorporated in its entirety herein. An embodiment of the overhead monorail system 50 is shown in FIG. 2. The overhead monorail system 50 includes a conveyor 14 and directors 56 for guiding the SMIF pods 12 between equipment front end modules (“EFEMS”).
By way of example only, the conveyor 14 may also include one or more cross sections which may be used as a short-cut to other areas of the bay 18 to temporarily remove pods 12 from the main conveyor loop without interrupting the traffic flow on the main loop. The configuration of the conveyor 14 is subject to considerable variation depending on the constraints of a particular manufacturing facility.
FIG. 3 illustrates one embodiment of a conventional conveyor 14. The conveyor includes a pair of rails 32, 34 for supporting the transport pod 12 as the pod 12 moves along the conveyor path. The drive rail 32 propels and optionally guides the pod 12 along the rails 32, 34. Propulsion power for moving the pod 12 is supplied via the drive rail 32. Power may be supplied to the drive rail 12 via conventional means. Alternatively, power may be supplied to the drive rail 32 by a power bus. Rail 34 is an idler or support rail for supporting the transport pod 12 such that the pod 12 is held in a level orientation as it is moved along the conveyor path. Optionally, the support rail 34, as opposed to the drive rail 32, may be used to guide the transfer pod 12 as it travels along the conveyor system 14.
Hoists or similar devices may be used to lower the pods onto the load port of the processing machine. In order to successfully transfer the pod from the monorail to the machine, the pod must be precisely aligned with the load port and lowered onto the port in a controlled manner such that any swing of the pod is minimized. After processing, the pod is raised and transported to the next machine. Repeatedly raising and lowering the pod is challenging.
All of the transport systems mentioned above require the wafers to travel within an isolated container, or SMIF pod, to ensure that the wafers are not contaminated by harmful particles. Every time a batch of wafers are transported to a new process tool, the pod must form a seal with the front end of the processing tool prior to opening the pod. Similarly, when the batch of wafers have been processed and replaced back into the pod, the pod door must be replaced before the pod may be transported to the next process tool.
When wafers are transported within a pod, the batch of wafers must remain with the same pod throughout the entire manufacturing process. Every time a wafer must be inspected or arrives at the next processing tool, the SMIF pod must form a seal with the tool to isolate the wafers from contaminants and the pod door must be removed before a robot may remove a wafer from the SMIF pod. Similarly, the robot must place the wafer back into the SMIF pod, and the SMIF pod must be sealed and charged, before the SMIF pod can continue onto the next processing tool. This is a very time consuming task.
Many challenges arise from using a transfer system that transports SMIF pods. Often, a vendor requires a quick turn-around time for a small batch of wafers. These wafers may not need to pass through all of the processing stations within the wafer fabrication facility. Without the ability to pass SMIF pods ahead of the small batch, the processing of the small batch cannot be accelerated. Wafers that must be transported within SMIF pods cannot be randomly dispatched
Ergonomic and safety issues coupled with the need for efficient and rapid material transport will be the major drivers in defining material handling systems for the 300 mm wafer generation and beyond. The automated material handling systems must have acceptable return on investment and must interface directly with all inline production equipment. With the increase in 300 mm equipment size, the utilization of floor space in the factory must improve. Solutions to provide higher wafer storage densities, short lead and install times, and better utilization of floor space through integration of process and metrology equipment must be developed.
It would be an advantage to integrate interbay and intrabay transport into one integrated system. Such a system would provide a direct, or tool-to-tool transport system. The throughput of wafers would be increased. The tool-to-tool transport system must be designed so that is can accommodate the extendibility, flexibility, and scalability demands on the factory.
Transporting individual wafers in a sealed environment, without the need for SMIF pods, would have several advantages. First of all, the throughout of the system could be greatly improved. Eliminating SMIF pods would allow a manufacturer to randomly dispatch wafers, accelerate the processing time of a wafer, and integrate metrology stations into the process sequence. Small lots of wafers could be easily processed and even be accelerated through the process sequence. The present invention provides these advantages.